Manufacturing process for small bulbs

ABSTRACT

The present invention provides a method of producing small bulbs to be used in electronic equipment, particularly high-quality uniform small bulbs by a simple process, which is suitable for mass production and yields partically no rejects. The method is characterized by a large number of bulbs and bead mounts which comprise such elements as a filament, a fuse piece, a semiconductor piece, a neon-tube electrode, or a lead switch electrode being assembled directly on a carbon plate jig with a uniform temperature distribution. The carbon plate jig is directly or indirectly heated, thereby sealing together the bulbs and the beads of the bead mounts with the jig which concurrently serves as heater.

United States Patent [191 Hamai May 20, 1975 [75] Inventor:

[73] Assignee: Hamai Denkyu Kogyo Kabushiki Kaisha, Tokyo, Japan [22]Filed: July 31, 1973 [21] Appl. No.: 384,306

Jituo Hamai, Tokyo, Japan 3,460,219 8/1969 Shiragaki 29/25.13 3,698,78410/1972 Hamai 3,698,785 10/1972 Hamai 316/19 Primary ExaminerRoy LakeAssistant Examiner-J. W. Davie Attorney, Agent, or FirmArmstrong,Nikaido & Wegner [57] ABSTRACT The present invention provides a methodof producing small bulbs to be used in electronic equipment,particularly high-quality uniform small bulbs by a simple process, whichis suitable for mass production and yields partically no rejects. Themethod is characterized by a large number of bulbs and bead mounts whichcomprise such elements as a filament, a fuse piece, a semi-conductorpiece, a neon-tube electrode, or a lead switch electrode being assembleddirectly on a carbon plate jig with a uniform temperature distribution.The carbon plate jig is directly or indirectly heated, thereby sealingtogether the bulbs and the beads of the bead mounts with the jig whichconcurrently serves as heater.

4 Claims, 9 Drawing Figures PATENTED NAYZOISYS SHEET 10F 3 FIG.2

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1 MANUFACTURING PROCESS FOR SMALL BULBS BACKGROUND OF THE INVENTION Itis important in the manufacture of small bulbs to assure perfect sealingof the bead of a bead mount in the bulb and to prevent leakage of anyimpure gas into the bulb to be sealed. For the mass production of suchsmall bulbs it is necessary to simplify the method and work so that thework can be finished as soon as possible; the products can be uniform inquality; and the yield of rejects can be minimized. Various proposalshave so far been made for manufacture of small bulbs by sealing togetherthe bulb and the bead of a bead mount within a vacuum.

There are, however, unavoidably many technical difficulties in themanufacture of such small bulbs with outer diameter 1-6.5 mm and length3.5- mm, such as assembling of bulb and bead of the bead mount to besealed together; adsorption of generated gases; or deterioration of thevacuum due to the generated gases.

Thus every mechanical method of sealing resulted in non-uniform orinferior products and manual techniques have been the only methodavailable, thus ruling out the possibility of mass production.

An improvement in this prior art technique is disclosed in the U.S. Pat.No. 3,698,784 by the inventor of the present invention.

This is an improvement over the conventional halfmechanized one in thatit can produce superior bulbs, and -40 units of them at one time. Butstill it has too many imperfections to be used for mass production; muchtime is needed for setting the parts; there must be secondary treatmentafter the primary treatment of the product; the unnecessary portion mustbe cut off from the secondary treated product; precaution must be takenin positioning the bead mount within the bulb to secure uniformity ofproducts; there is low productivity per unit area in unit time; andcertain skill is required for the work.

SUMMARY OF THE INVENTION The present invention provides a method ofproducing 1000 to 2000 small bulbs or even more at a time, the bulbsbeing uniform, of high quality with no yield of rejects in a simplemechanical operation with all the drawbacks in the above-mentioned priorart being eliminated.

To attain the intended object, in the present invention a carbon platejig is set up in a heat-insulated box lined with metal reflector andheat shield or in a similar box enclosed within a vacuum. On said carbonplate jig are assembled a large number of bulbs and bead mounts attachedwith a filament, a fuse piece, a semiconductor piece, a neon-tubeelectrode and a leadswitch electrode. The carbon plate jig is equippedwith stepped holes for positioning bulb-bead mount assemblies', and, inthe case of the jig being directly heated by electric current. the jighas near both ends a large number of heat-dam holes for equalizing thetemperature distribution approximately over the whole surface.

The bulb and the bead of a bead mount are to be sealed together by theheat generated from said carbon plate jig. For the purpose of heatingthis jig, the resistance heat generated by the direct passage of thecurrent or the heated emitted from a quartz bulb infrared lamp or froman iodine lamp installed within the heatinsulated box is absorbed by thejig.

For the purpose of preventing impure gases from collecting in theheat-insulated box, the temperature in the heat-insulated box isprogressively raised and by some appropriate means the impure gases arecompletely driven out of the heat-insulated box. After the heatinsulatedbox has been evacuated, the heat generation from the carbon plate jig isintensified in a short time, thereby sealing together the bulb and thehead of a bead mount. Lastly, the heat-insulated box is gradually cooledand with an atmospheric pressure restored therein. the final products,i.e., finished small bulbs are taken out of the box.

BRIEF DESCRIPTION OF THE DRAWINGS The manufacturing process of smallbulbs according to the present invention will become apparent by readingthe following detailed account in conjunction with the attacheddrawings.

In the attached drawings, FIG. I illustrates one embodiment of thedevice for manufacturing small bulbs in accordance with the process ofthe present invention.

FIG. 2 shows the embodiment of FIG. 1 in greater detail with a partialsection.

FIG. 3 is a plan view of the main body of the heatinsulated box and apartially cut away carbon plate jig in FIG. 2.

FIG. 4 is a partial enlargement of the carbon plate jig in FIG. 2.

FIG. 5 illustrates another embodiment of the device for manufacturingsmall bulbs in accordance with the process of the present invention.

FIG. 6 shows the embodiment of FIG. 5 in greater detail with a partialsection.

FIG. 7 is a plan view of the main body of the heatinsulated box and apartially cutaway carbon plate jig in FIG. 6.

FIG. 8 is a partial enlargement of the carbon plate jig in FIG. 6.

FIG. 9 is a sectional view of a finished bulb.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of the device formanufacturing small bulbs in accordance with the present invention is tobe described referring to the corresponding drawings. In all thedrawings, same symbols represent same parts.

In FIGS. 1, 2, 3, 4 and 9, a bead 3 is mounted on a pair of lead wires 1and 2 separated by a specified gap. Between the tops of said wires 1 and2 is stretched a filament 4, thus completing a bead mount A.

Next, a bead mount A with the filament 4 on the upper side is, fittedinto each step 6a of a plurality of stepped holes 6. The holes 6 areprovided on a rectangular carbon plate jig S; and from above, a bulb 7of a specified size with its top closed and its bottom open is fitted tothe step 6a so as to embrace the bead 3 of the bead mount A. Thus theassembling by positioning the bulb 7 and the bead mount A is completed.The carbon plate jig 5 thus assembled is placed above the main body 9 ofthe heat-insulated box set on the stand 8 within the vacuum box B, withthe electrode junction holes 10 at both ends holding the electrodes 11in such a manner that said jig may not come into contact with said mainbody 9. The cover 13 for the heat-insulated box has a notched hole 12 sobored as not to touch the carbon plate jig 5 is put on the top of themain body 9 of the heat-insulated box.

Next, the heaters for supplemental heating l4 and fixed to both sides ofthe main body 9 and the cover 13 of the heat-insulated box areseparately connected. The cap terminals at their ends 17, 18, 19 and 20are connected to the electrodes 16 separately provided.

The whole structure is then covered; the lid 21 is put on the vacuum boxB; and the electrodes 11 and 16 jutting out from the base 22 of thevacuum box B through the insulators 23 and 24 are connected to theappropriate power sources. Suction is used through the vent hole 25provided on the base 22, the vacuum box B and the heat-insulated box 9and 13 are evacuated and the sucking state continues to be maintained.

In this state the power supply to the heaters for supplemental heatingl4 and 15 is switched ON to heat up the heat-insulated box 9 and 13 fromboth sides. Then the power supply to the carbon plate jig 5 is switchedON to maintain a constant temperature of, say, 500C which acceleratesthe generation of impure gases out of the metal parts inside theheat-insulated box 9 and 13. When within the heat-insulated box 9 and 13impure gases are generated in sufflcient quantities and they areexpelled out of the vacuum box B, the power supplied to the carbon platejig 5 is increased to raise the temperature in the heat-insulated box 9and 13 to nearly the glass-softening point, say, to 550C, thereby toinduce possible generation of more of impure gases. These gases aredriven out of the vacuum box B. After complete removal of the impuregases generated in the heat-insulated box 9 and 13 from the vacuum boxB, the power supplied to the carbon plate jig 5 is further increased toraise the temperature of the carbon plate jig 5 up to the glass-meltingpoint of, say, 600C in a short time, thereby sealing together the bulb 7and the bead 3 of the bead mount A.

Subsequently the power supply to the heaters for supplemental heating l4and 15 and to the carbon plate jig 5 is turned OFF and the condition isleft as it is for a brief time, or the heat-insulated box 9 and 13 isgradually cooled by introducing nitrogen gas into the vacuum box B andthe heat-insulated box 9 and 13 through the vent hole 25.

After this cooling, the air is admitted into the vacuum box B throughsaid hole 25, thereby restoring the atmospheric pressure therein. Thelid 21 of the vacuum box B is taken off the base 22; the cap terminals18 and 20 are disconnected from the electrodes 16; and the cover 13 ofthe heat-insulated box is taken off the main body of said box. Then thecarbon plate jig 5 is unfastened from the electrodes 11; and a finishedproduct, i.e, a small bulb C with the bulb 7 and the bead 3 of the beadmount A sealed together, is taken out, thus completing the wholeprocess.

In this embodiment of manufacturing small bulbs, however, a few problemsarise. One is a problem of electrical characteristic that when thecurrent flows in the carbon plate jig 5, the heat is generated from thecentral portion due to the resistance; and thus even when theglass-melting point is attained at the central portion, both sides of itare still below of the glassmelting point. Thus, the end portions of thecarbon plate jig 5 cannot be as hot as the central portion, because ofthe electrical resistance and the escape of heat to the electrodejunctions. For this reason, even if the parts-fitting holes 6 areprovided practically all over the surface of the carbon jig 5, not allof the products will be of uniform quality and accordingly the areaassuring uniformity of products is limited to the central portion.Therefore, the method may be more mass-productive than the conventionalone, but the mass-productivity realized will not be as great as expectedfrom the present invention as one of its objects. This problem hashowever been solved as follows: at both ends of the carbon plate jigalarge number of tiny holes 26 are bored and the current from per unitarea of these portions is enriched, while the heat dissipation towardboth ends in heated carbon plate jig 5 is prevented by the electricalresistance which has been made as high as possible, thereby widening theextent of equalized temperature distribution in the carbon plate jig 5itself. Both sides of the main body 9 and the cover 13 of theheatinsulated box are provided with the supplemental heaters 14 and 15to compensate for the loss of heat to both ends of the carbon plate jig5, the supplemental heaters being composed of common resistance heaterswherein a nichrome wire penetrates a quartz glass tube.

The heat-insulated box 9 and 13 is lined with heatinsulating,heat-resistant sintered plates 27 and with one or more mirror-finishedheat-resistant reflectors 28 of such metal as molybdenum or stainlesssteel which is least likely to emit metal gases. This enablesintensifying the temperature rise on the carbon plate jig in theheat-insulated box 9 and 13 and suppressing the temperature rise outsideof the heat-insulated box 9 and 13.

On the bottom of the main body 9 of the heatinsulated box there aremounted, on both sides of the central portion, mirror-finished splitmetal reflectors 29 of molybdenum or stainless steel respectively with areflecting inclination between a set of supports 30. The heat of thecentral portion can thereby be reflected in both directions to improvethe uniformity of temperature distribution within the heat-insulated box9 and 13.

According to this method, the temperature distribution within theheat-insulated box 9 and 13 and the temperature distribution of thecarbon plate jig 5 over a wide area extending from the center of the jigto the proximate ends thereof, can be equalized and it becomes possibleto manufacture uniform products in great quantities at a time.

For instance, it has been experimentally confirmed that all the productswill be uniform in quality, even when small bulbs are produced using1029 holes 6 of 3.2 mm diameter provided on a rectangular carbon platejig 5 measuring 35 cm long and 10 cm wide.

in the drawings the sintered plate 27 and the metal reflector 28 are setwith an adequate fine gap between them. The main body 9 and the cover 13of the heatinsulated box are fixed by means of a metal clamp 31. Anairtight rubber ring 32 is fitted into the groove 33 cut on the base 22of the vacuum box B, thereby sealing the lid 21 of the vacuum box Bairtight with the base 22.

Another problem is raised by degradation of the product quality throughinfiltration into the bulb of the impure gases such as metal gases whichare generated from the heaters or from outside and inside of theheatinsulated box.

Generally in the manufacture of such small bulbs, emission of impuregases from the metal parts of the device is unavoidable, because thedevice itself is exposed to high temperatures.

For this reason when the bulb and the bead of a bead mount are sealedtogether, impure gases are entrapped within the bulb, resulting in poorevacuation or rejection of the product on account of being taintedthrough gas adsorption.

[n the present embodiment, the problem has been solved as follows. Thejig 5 for assembling the bulb 7 and the bead mount A is fabricated ofcarbon and the jig 5 itself is heated for sealing them, therebyeliminating the possibility of impure gases being generated from theheater itself.

The heat-resistant reflector 28 which lines the heatinsulated box 9 and13 is made of a mirror-finished heat-resistant metal such as molybdenumor stainless steel, thereby minimizing the emission of impure gases.

The inside walls of the heat-insulated box 9 and 13 include a sinteredheat-resistant plate 27 and thereby the outside surface of theheat-insulated box and the objects outside of it can be kept as cold aspossible, so that a metal gas-emitting temperature may not be attained.

The heating conditions are such that at first the temperature of theheat-insulated box 9 and 13 including the carbon plate jig 5 is elevatedto, say, 500C. This temperature is maintained for some time to inducegas emission from the objects inside of the box. The emitted gas isexhausted through the vent hole 34 provided at mid-bottom of the mainbody 9 of the heat-insulated box and through the vent hole 25 of thevacuum box B, thereby equalizing the atmospheric conditions within theheat-insulated box 9 and 13. Next, the temperature is brought up closeto the glass-melting point and the gas exhaustion is continued.Following the complete elimination of gas, the temperature is raised tothe glass-melting point in a brief time, thereby sealing together thebulb 7 and the bead 3 of a bead mount A.

According to this method, the yield of impure gases in the heatinsulatedbox 9 and 13 is extremely low; and the impure gases generated outside ofthe box as well as inside of it can be throughly driven out before thesealing of bulb and bead, because the exhaustion of gas is continuouswhile the temperature within the heatinsulated box 9 and 13 is beingprogressively increased. Thus the leakage of impure gas into the bulb 7can be prevented.

The sintered plate 27 and the metal reflector 28 which cover the bottomof the main body 9 of the heatinsulated box are bored with a largenumber of tiny holes 35 located in a staggered fashion for betterreflectivity. The impure gases generated in the heat-insulated box 9 and13 can be expelled through these tiny holes and then through the venthole 25 in the bottom of the main body 9 of the heat-insulated box.

Another embodiment of the present invention is to be described referringto FIGS. 5, 6, 7, 8 and 9. The method is the same as in the firstembodiment except that in the second embodiment, the carbon plate jig isheated by infrared rays and the heat absorbed by the carbon plate jigseals together the bulb 7 and the bead 3 of a bead mount A. The infraredreflection box has the same structure as the heat-insulated box but isnot enclosed in a vacuum box B.

The manufacturing process of small bulbs C in the second example is tobe described referring to FIGS 5-9. In these figures and in those forthe first example, same symbols denote the same parts.

At first, in the same manner as in the first embodiment, bulbs 7 andbead mounts A are assembled on the steps 6a of numerous stepped holes 6for positioning, which are provided on a rectangular carbon plate jig38, which is small enough to go into the infrared reflection box 36 and37. These assemblies are placed on the sintered heat-resistant plate 27at the top of the main body 36 of the infrared reflection box and thelid 37 of the infrared reflection box with a flange 42 which closelyfits the top fringe groove 41 of the main body 36 of the infraredreflection box is placed on top.

Then the terminals of nine infrared heaters consisting of quartz tubeinfrared lamps or iodine lamps installed within the main body 36 of theinfrared reflection box installed on the stand 40 of the foundation 39are coupled to conductive bars 44 and 45; and the terminals of saidconductive bars 44 and 45. The cap terminals 46 and 47 are attached tothe terminals of the conductive bars 44 and 45 projecting through vacuumlead terminals of the prior art out of the main body 36 of the infraredreflection box and are connected to the electrodes 50 and 51 fittedthrough the insulators 48 and 49 to the foundation 39.

Next the bottom ends of said electrodes 50 and 51 are connected to thepower supply. Then using the common method of suction, the infraredreflection box 36 and 37 is evacuated through the vent hole 34 at aboutmid-bottom of the main body 36 of the infrared reflection box andthrough the vent pipe 52 penetrating the foundation 39. The suction iscontinuous. In this state the power supply to the infrared heater 43 isturned ON and the heating is continued until the impure gas-emittingtemperature, say, 500C is reached on the metal parts within the infraredreflection box 36 and 37.

In the meantime, the carbon plate jig 38 becomes steadily hotter thenthe infrared reflection box 36, 37, on account of its heat absorptioncharacteristic, absorbing the heat from the infrared heater 43 andreceiving the heat reflected from the metal reflector 28 similar to thefirst embodiment and from a split metal reflector 29. In two minutesafter the temperature in the infrared reflection box 36 and 37 hasreached 600C, the temperature of the carbon plate jig 38 reaches theglass-melting point, as experimentally confirmed.

Accordingly in about two minutes of this temperature being attained inthe infrared reflection box 36 and 37, the sealing of the bulb 7 and thebead mount A is completed. Immediately after passage of this time thepower supply to the infrared heater 43 is cut off; and the infraredreflection box 36 and 37 is gradually cooled by introducing nitrogen gastherein through the vent pipe 52. When the cooling is finished, the airis admitted through the vent pipe 52 into the infrared reflection box 36and 37 to restore the atmospheric pressure therein and the lid 37 istaken off the main body 36.

Then the carbon plate jig 38 :is taken out of the main body 36 of theinfrared reflection box and from said jig 38 finished products, i.e.,small bulbs C with sealed assemblies of bulb 7 and bead 3 of bead mountA are obtained, thus completing the whole process.

In this embodiment, unlike in the first embodiment, the infraredreflection box 36 and 37 is not placed in a vacuum box B, but the objectof the present invention will be accomplished all the same whether sucha vacuum box B is used or not.

Meanwhile, known means of prior art can be adequately selected forairtight fitting of the main body 36 and the lid 37 of the infraredreflection box; for providing the infrared heaters 43; for limiting theignition of said infrared heaters 43 before the bulb-bead sealingtemperature is reached and then igniting all of the heaters to attainthe sealing temperature; or for controlling the temperature of thecarbon plate jig.

When in accordance with the method of this embodiment 1029 sets of bulbs7 measuring 3.2 mm in diameter were assembled on a rectangular carbonplate jig 38 of 18 cm length and 10 cm width and the sealing of bulb 7and bead mount A was executed using 12 100V, 500W infrared lamps, all ofthe 1029 small bulbs C obtained turned out satisfactory with a perfectseal, regardless of the positions where they were fitted on the carbonplate jig 38.

In the first and second embodiments, the degree of vacuum in the vacuumbox B, the heat-insulated box 9 and 13 and the infrared reflection box36 and 37; the temperature of the heater; and the heating duration mayvary depending on the size and wall thickness of small bulbs to beproduced or on the bead of the bead mount, but these conditions can beappropriately set by the known technical means.

ln the described embodiments, an increase in dimensions of the devicefor a more efficient mass production of bulbs or selection of apparatusfor execution of the present invention are obvious modifications.

As described above the present invention is characterized in that thedevice is simple, calling for no skill for its operation. The productsare of equal quality with no variation, because the bulb and the beadmount can be properly set by merely attaching them to the steps of theparts-fitting holes provided on the carbon plate jig, and thereby thebead mount can be exactly centered relative to the bulb.

Furthermore, the carbon plate jig, which serves for both assembling thebulb and the bead mount and heating to seal them together, can minimizethe generation of impure gases like metal gass as compared with ametalic jig. On the other hand, in the present invention thegas-emitting temperature is maintained for some time; and the impuregases generated in that time are driven out before the sealing of bulband bead mount takes place. As the result a product of high quality withno impure gas left in the bulb can be produced.

Further, the invented process involves few steps and the sealing of bulband bulb mount can be simply executed. ln consequence no rejects areproduced and this contributes to cost reduction of production.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Thepresently disclosed embodiments are therefore to be considered in allrespects as illustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims rather than the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

What is claimed is:

1. A method of making small bulbs by fusing bead mounts with elementstherein to a bulb envelope comprising:

a. inserting a plurality of said bead mounts into a plurality of holesin a carbon jig plate;

b. placing a bulb envelope in contact with each of said bead mounts;

c. placing said carbon jig plate with the plurality of unsealed bulbsassembled thereon within a heat insulated box;

d. evacuating said heat insulated box;

e. heating said carbon jig plate to a temperature for inducing thegeneration of impure gases and withdrawing said impure gases, furtherraising the temperature to a value close to the softening point of saidbulb envelopes and then further heating said carbon jig plate to atemperature sufficient to cause the fusing of said bead mounts and saidbulb envelopes; and

f. gradually cooling the inside of said heat insulated box.

2. The method of claim 1 wherein heating said carbon plate jig includespassing an electric current through said carbon plate jig and therebygenerating heat due to the resistance thereof.

3. The method of claim 1 wherein heating said carbon plate jig includesexposing said carbon plate jig to infrared radiation.

4. The method fo claim 1, wherein heating said carbon plate jig includesinternally reflecting the heat in said box means back to said carbonplate jig.

1. A method of making small bulbs by fusing bead mounts with elementstherein to a bulb envelope comprising: a. inserting a plurality of saidbead mounts into a plurality of holes in a carbon jig plate; b. placinga bulb envelope in contact with each of said bead mounts; c. placingsaid carbon jig plate with the plurality of unsealed bulbs assembledthereon within a heat insulated box; d. evacuating said heat insulatedbox; e. heating said carbon jig plate to a temperature for inducing thegeneration of impure gases and withdrawing said impure gases, furtherraising the temperature to a value close to the softening point of saidbulb envelopes and then further heating said carbon jig plate to atemperature sufficient to cause the fusing of said bead mounts and saidbulb envelopes; and f. gradually cooling the inside of said heatinsulated box.
 2. The method of claim 1 wherein heating said carbonplate jig includes passing an electric current through said carbon platejig and thereby generating heat due to the resistance thereof.
 3. Themethod of claim 1 wherein heating said carbon plate jig includesexposing said carbon plate jig to infrared radiation.
 4. The method foclaim 1, wherein heating said carbon plate jig includes internallyreflecting the heat in said box means back to said carbon plate jig.